Schmidt optical system suitable for a panoramic scanning camera including means to compensate for variations in off-axis magnification

ABSTRACT

The subject invention provides an optical system that is particularly well suited for use in a panoramic scanning camera. It has a primary image-forming system followed by a Schmidt system having positive and negative components. A pair of correcting prisms can be placed between the primary and Schmidt systems. An aspheric surface on one of the prisms is imaged by refraction into the vicinity of the Schmidt components. Components to correct variations in off-axis magnification are also included.

uulwu Dial Baker 1 y 7 y Q/ 1 July 25, 1972 [s41 SCHMIDT OPTICAL SYSTEM[56] Reterences Cited SUITABLE FOR A PANORAMIC SCANNING CAMERA INCLUDINGUN'TED STATES PATENTS MEANS T0 COMPENSATE FOR 2,522,390 9/l950 McCarthy..350/l7$ SL VARIATIONS IN OFILAXIS 3,454.32l 7/ I969 Klein ..350/|84 X3, l 70,984 Rosenberger el al l 84 [72] Inventor: James G. Baker,Winchester, Mass. Primary Examiner-David Schonberg AssistantExaminer-Paul A. Sacher [73 cam'mdge' Mass Attorney-Brown and Mikulkaand William D. Roberson [22] Filed: Dec. 15, 1969 211 App]. No.: 889,787[57] ABSTRACT The subject invention provides an optical system that ispar- Appuuu ticularly well suited for use in a panoramic scanningcamera. It [62] Division of Ser. No. 680,621, Nov. 6, I967, Pat. No. hasa primary image-forming system followed by a Schmidt 3,548,729. systemhaving positive and negative components. A pair of correcting prisms canbe placed between the primary and [52] U.S. Cl. ..350/l84, 350/l 86,350/189, Schmidt systems. An aspheric surface on one of the prisms is/202. 350/239 imaged by refraction into the vicinity of the Schmidt com-[5 l 1 Int. Cl. p nents componcnts [d con-cc variations in off-axismgsnifi- 84, 200, cation are also inc|udd 10 Claim, 4 Drawing FiguresPATENTED L 1 ma EM wm m. m 5 F- M A v 3 Y B G F and W am ATTORNEYSSCHMIDT OPTICAL SYSTEM SUITABLE FOR A PANORAMIC SCANNING CAMERAINCLUDING MEANS TO COMPENSATE FOR VARIATIONS IN OFF-AXIS MAGNIFICA'I'IONThis is a division of copending Application Ser. No. 680,621, filed Nov.6, 1967, now U.S. Pat. No. 3,548,729.

BACKGROUND AND SUMMARY OF THE DISCLOSURE The present invention relatesto photographic optics and, more particularly, to a corrected opticalsystem for a shallow camera that is characterized by an extremely shortdimension between the forward position of the first refracting surfaceand the rearward position of the final image surface. Such an opticalsystem is adapted for incorporation into a hand held camera, the heightand width of which are sufficiently large to accommodate a full sizephotographic frame that may be developed directly by diffusion transferor the like but the thickness of which is sufi'lciently small to permitthe camera to be carried unobtrusively in a clothing pocket or the like.Prior cameras having a like shallow front to back depth have beencharacterized by relatively small images because of the usuallyoccurring relationships between lens diameter and focal length. In onetype of camera incorporating a lens system of the present invention (seeU.S. Patent Application Ser. No. 549,961, filed May 31, I966, now U.S.Pat. No. 3,405,619, in the name of Edwin H. Land) the optical system ispanoramic in operation. In one form, such a camera comprises (at one endof the camera) a pivotal scanning mirror and (at the other end of thecamera) a slit, past which the photosensitive film is moved at a ratewith which the scanning mirror rate is synchronized in order tosynthesize a complete image from a continuous sequence of increments. Inthe design of such a compact system, it has been found that severedifficulties are encountered in attempting to compensate for perspectivedistortions and to achieve good image quality by correction ofaberrations.

Primary objects of the present invention, for reasons that will beexplained in detail below, are: to provide a corrected optical systemthat is adapted in one form for application to panoramic scan operationin a hand held camera characterized by an X-direction along whichradiation from a field of view is received, a Y-direction with which aslit, that defines successive increments of a panoramic image, isparallel and a Z-direction with respect to which relative motion occursbetween the slit and a photographic film at the image surface; toprovide an optical system of the foregoing type in which an objectivelens array includes a positive and a negative lens component (analogousto the first and second lens components of a Cooke triplet) forrefracting light from a scanning mirror in object space in such a way asto introduce a substantially collimated flux into the remainder of thesystem; to provide an optical system of the foregoing type containing atleast a pair of opposed prisms which pivot in synchronism and in afunctional relationship with the relative motion between the slit andthe photographic film to compensate for variations in off axismagnification resulting perspectively from operation of the scanningmirror; to provide a Schmidt type lens array with residual aberrationsthat are substantially opposite those of the objective lens array so asto combine with the objective lens array to produce excellent correctionfor various chromatic and seidel aberrations; and to provide adjacent tothe photographic image surface a zoom lens array with low net power thatpermits variation in the focal length of the system by virtue ofrelatively movable high power components which provide appreciablesensitivity to spatial variation without destroying image quality andwithout movement of the critically positioned forward refracting surfaceand photographic image surface. Although the foregoing components areshown herein as being useful in a panoramic hand held camera, it is tobe understood that certain of the specific relationships are useful inother arrangements where similar problems of aberration correction areencountered.

Other objects of the present invention will in part be obvious and willin part appear hereinafter.

The invention accordingly comprises the apparatus possessing theconstruction, combination of elements and arrangement in parts, whichare exemplified in the following detailed disclosure, the scope of whichwill be indicated in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of thenature and objects of the present invention, reference is made to thefollowing detailed description, taken in connection with theaccompanying drawings wherein:

FIG. I is a perspective view of a shallow camera incorporating a lenssystem embodying the present invention;

FIG. 2 is an unfolded, cross-sectional, layout view of the lens systemof FIG. 1;

FIG. 3 is a view of the layout of FIG. 2, in a cross-sectional plane atright angles to that of FIG. 2; and

FIG. 4 is a diagram illustrating certain principles of the presentinvention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Generally, the cameraof FIG. 1 comprises a housing 20, shown in phantom lines, that enclosesand supports the optical and photographic components. The photographiccomponents for example include a photosensitive stratum .22 and an imagereceptive stratum 24, the former being constituted for advancementrelative to the optical system in a manner to be described below and thelatter being constituted for superposition with the latter in thepresence of an interposed processing fluid 26, by operation of a pair ofpressure rollers 28, 30. The resulting sandwich is ejected through aslot 32 at an extremity of the camera and the resulting picture may bestripped from the sandwich thereafter. Details of the compositions ofphotosensitive stratum 22, image receptive stratum 24 and processingfluid 26 are described in U.S. Pat. No. 2,543,l8l, issued on Feb. 27,1951 in the name of Edwin H. Land. It will be understood that otherconfigurations of photosensitive and receiving strata are contemplated,one such configuration specifically including the photosensitive andreceiving strata in an integrated sheet.

The parts of the illustrated optical system now will be describedbriefly to provide preliminary comprehension of overall function andoperation, as a basis for the detailed explanation to follow. As shownin FIG. 1, this system comprises: a window 40 which communicates theoptical system with the objective view along an X-direction 41; ascanning minor 42, which varies the attitude of the optical system withrespect to the field of view while deflecting the optical path along aY-direction 43; an objective lens array, including a positive lens 44and a negative lens 46, for introducing a collimated flux to theremainder of the system; a pair of oppositely-rotatable prisms 48, 50,synchronized with and functionally related to the motion of scanningmirror 42 to compensate for variations in off axis magnification fromoperation of the scanning mirror; a trapezoidal, plane mirror (oralternatively a totally internally reflecting prism) 52 for deflectingthe optical path along a Z-direction 53; a cemented doublet 54, S6constituting part of a Schmidt type lens array, in association with anasphen'c surface at the rear of prism 50, (or alternatively at the frontof prism 48), having residual aberrations that are substantiallyopposite those of objective lens array 44, 46 so as to combine with theobjective lens array to produce excellent correction for variouschromatic and seidel aberrations; a zoom lens array having a negativelens 58 and a positive lens 60, the refracting surfaces of which aredisposed in proximity with a slit 38 along the Y-direction substantiallythroughout the width of the camera but are restricted in the directionof the X-direction and an elongated plane mirror 61 for deflecting theoptical path along the X-direction to the image surface and thephotosensitive stratum therein. In operation, a suitable drive 64, 66,70 rotates scanning mirror 42, oppositely pivots prisms 48, 50 androtates pressure rollers 28, 30 in order to advance photosensitivestratum 22 past slit 38 and spreads processing fluid 26 betweenphotosensitive stratum 22 and print receptive stratum 24 as the sandwichformed thereby emerges from a light-tight slot 32 in housing 20. Asshown, drive 64, 66, 70 includes three mechanically isolated, miniaturetorque motors, that are powered by a dry cell 74 under the control of asolid state circuit 76. Following a development period, conventionallyranging between seconds and a minute, the photosensitive and imagereceptive strata are stripped apart to reveal the regular-sizephotographic print. The forward focal distance is variable by simplyadjusting manual knob 68 which controls the positions of negative lens46, cemented doublet 54, 56 and zoom lens elements 58, 60. The mountingswhich establish these positions are connected by a suitable linkage (notshown). A shutter (not shown) at window 40, in one form, assists scanmirror 42 in excluding undesired light from within the camera housingand a closure (not shown) at the back of the camera housing enablesreloading thereof conveniently.

The structure and function of the components of the lens system now willbe described in detail.

Objective Lens Group 44, 46 and Correcting Prisms 48, 50 mirror Althoughthe depth of the illustrated camera from forward refracting surface torearward focal plane is unusually shallow, the lens system axially isunusually long for its focal length. The manner in which this unusuallength is achieved will be described below. The reasons for this unusuallength are the specified depth of the housing as being less than oneinch, the specified position of the entrance window as being located atthe upper left hand corner as the user sees it from behind, thespecified use of transfer diffusion photographic materials, thespecified choice of a fixed image size and position which, for infiniteobject distance, corresponds to an approximately five inch focal length(for a wide range of object distances), the space needed for diagonalsweep mirror 42, the space needed for trapezoidal mirror 52, the spaceneeded for elongated mirror 61 and the specified slit position.

A panoramic camera of the type disclosed introduces a number of problemsnot ordinarily encountered in snapshot photography. For example, in thepresent case, photosensitive stratum 22 is to be moved at a constantrate past slit 38 while lying in a plane at original anglessubstantially with respect to original X-direction 41. Ordinarily, aflat field lens system produces an image on a photosensitive stratum atthe focal plane. However, in the present case, when the field of view isscanned by such means as diagonal sweep mirror 42, in the meridionalplane, the image rate is exactly that of the photosensitive stratum rateonly at the center of the slit. With a reasonably narrow slit width, inthe present case a maximum of 0.4 inches, there is a slight butacceptable blurring which is caused by the slight difierence between thepositions of points along an arcuate cylindrical surface defined by thescan mirror about its axis and the corresponding positions of pointsalong a plane that would be defined by the operation of the lens systemitself. Along the length of slit, it obviously is necessary that theoptical design produce a flat image in the Z-direction and that thedistortion over the full length of the slit be held to say 1*: 1 percentof the mean value adopted for the entire panoramic image. To thisextent, the optical design for this panoramic camera becomes similar tothat of a snapshot camera. However, a snapshot camera would require awider field inasmuch as the diagonal of a square image, for example,would be l.4 times the length or width of the image. The opti- As shownin FIG. 2, the objective lens array includes window 40, scanning mirror42, positive lens element 44 and negative lens element 46. By design.for an adopted means object distance of 25 focal lengths, the raysemerging from negative lens element 46 are nearly or accurately parallelin order to minimize aberrations that would otherwise result ontransmission through correcting prisms 48, 50 to be described in detailbelow. Although strict parallelism could be obtained by the use of anaspheric surface forwardly of prism 48, it is not essential owing toreasonable tolerances permitted by the operating parameters of theillustrated optical system, namely a five inch focal length, an f/8speed and a 45 line pair per millimeter resolution, which areappropriate for good hand photography. It is to be understood thatprisms 48, 50 may be positioned at positions along the axis other thanthe positions shown without change in principle of operation.

Prisms 48, 50 are provided in response to the fact that a panoramiccamera causes the image to contain a distorted perspective for normalpurposes, namely, that which a pinhole camera would produce on a stripof film lying on a right circular cylindrical surface centered at thepinhole. As shown in FIG. 3, in a panoramic camera, a grid or reseau inobject space projects into a planar array where the previously straighthorizontal lines become curved as at 80 toward the meridional plane ofthe scanned picture from above and below, the amount of the curvaturedepending on the cosine of the offaxis angle. The vertical grid lines inobject space remain vertical as at 82 but are compressed on either sideof the axis toward a central line by an amount depending on the cosinesquare of the field angle, insofar as the magnification locally isconcerned, but by a displacement proportional to the difference of thetangent and the arc of the angle insofar as the actual absolutedisplacement is concerned. The present optical system is intended tocompensate for this cylindrical projection error by means both of a zoomaction depending on the off-axis angle, as will be described below, andby a pivoting of prisms 48, 50. Prisms 48, 50 are introduced here inorder to obtain a variable angular magnification in the meridional planeof the lens system. Parallel light refracted through such a prism pairat so-called minimum deviation, where each of the prisms refracts in anopposite sense with respect to the other, emerges accurately paralleland with unchanged magnification of the angular subtense of any objectviewed in the beam. That is to say, if one looked through the prism pairat a distant object for example, no change in apparent size would beobserved. The function of the prisms is to cause refraction to occuraway from the minimum deviation but through each prism equally andoppositely so that the emergent light will remain parallel but so thatthe angular subtense of any distant object viewed through the prism pairwill be altered by a calculable amount. It is essential that the prismsbe arranged to produce equal and opposite refractions in order that nolateral color dispersion be introduced into the emergent beam. That is,entering white light must emerge as white light, undispersed.

Prism pair 48, 50 is at minimum deviation at the center of the scan,that is, for the center strip of the panoramic picture. Off center,progressively, the prism pair produces in an angular sense a requisitechange in magnification that combines with the following components ofthe optical system to yield a magnified image at slit 38 which be designbecomes a single cosine correction factor in the meridional plane of thescan. Thus, the cosine square error is reduced to a single cosine errorto match the remaining single cosine error in the directionperpendicular to the direction of movement of the photosensitivestratum.

Prisms 48, 50 must operate in parallel or nearly parallel cal design ofthe contemplated panoramic camera need only light in order not tointroduce additional astigmatism into the cover the width of the imagesince the length is generated by the scanning operation, and no diagonaldimension is encompassed by the optical system. The optical system isshown in FIG. 2 as being unfolded along a single axis for ease ofexplanation.

optical image at the beginning or end of the scan. At minimum deviationfor the center of the field, there is no appreciable astigmatism andwould be none even if the light were not parallel. The prisms pivotabout axes 82, 84 by equal and opposite amounts from their positions atthe center of the field (mid-point of the scan action) where they are atminimum deviation.

It should be noted that in such a prism pair arrangement, full symmetrynecessarily is lacking. The reason for the slight asymmetry is that,although the required image enlargement both at the beginning and end ofthe scan is achievable as described, the following factors contribute tothe final effect. It is true that the prism pair at the beginning and atthe end of the scan occupy positions analogously away from the minimumdeviation. However, the rate of change, across increments (as determinedby the width of slit 38) of the field being scanned, is increased at theinitial or final increments of the image and is decreased at oppositelylocated increments of the image depending on which of the two relativepivotal relationships for pair of prisms 48, 50 is selected. For anarrow slit of the type herein contemplated, say 0.4 inch in maximumwidth, the problem is well within acceptable limits. For a wide slit,there might be no additional blurring action one side of center but adouble blurring action on the other side. In one alternative form of theinvention, such blurring with a relatively wide slit is eliminated by asecond prism pair, the motions of which are opposite correspondingmotions of the first prism pair. Also, in alternative forms of theoptical system, prisms 48, 50 are moved either to a position immediatelypreceding positive lens 44 or to a position immediately preceding sweepmirror 42, without change in function. In another alternative form ofthe present embodiment, objective lens array 44, 46 is pivoted about apoint on the optical axis appropriately between lens 44 and lens 46 toobtain additional outward distortion off-axis as a function of scanangle in order further to compensate the cylindrical projectionaberrations.

Schmidt Lens Array 54, 56 and Asperic Surface R With reference now toSchmidt type lens array 54, 56, it will be recalled that the so-calledSchmidt optical system employs two principles. The first is that ofsymmetry of reflecting or refracting surfaces about a center ofcurvature. The second is that of positioning a correcting surface at thecenter of curvature to remove spherical aberration over a wide field ofview. In the present Schmidt arrangement, the indices of refraction ofcemented elements 54, 56 are either identical at a mean wave length orso nearly so that residual aberrations are acceptable for thephotography to be achieved. The initial surface of lens 54 is taken tobe plano or sufficiently so that the residual aberrations areacceptable. Under these conditions, the center of curvature of the rearsurface of lens 56 is taken to lie by refraction at the rear vertex ofprism 50. If one were to put an artificial star point as a source oflight at this rear vertex 86, the rays after refraction through lenses54, 56, in a mean wave-length, would emerge as radii of the rearspherical surface of lens 56. To complete the Schmidt lens arrangement,the rear surface of prism 50 is aspheric in such a way as to produce asharply focused axial image at the final image plane of the system forthe full f/8 beam. Even though prism 50 rotates about axis 84 which isthrough vertex 86, the aspheric is so weak optically that no harmfulaberrations are introduced into the final image. As indicated above, inan alternative embodiment the aspheric surface and the center ofcurvature are at the front face of prism 48. In another alternativeembodiment, prisms 48, 50 are replaced by a substantially plane parallelelement, one or both of the surfaces of which are aspheric.

Schmidt type lens array 54, 56, together with its associated asphericsurface at 86, comprise a well corrected optical system except for somecurvature of field, a large inward or barrel distortion and some coloraberration. Similarly, objective lens array 44, 46 is an equally wellcorrected optical system but with opposite curvature of field, anoutward or pincushion distortion and opposite color aberration. The twoarrays in tandem thus produce a flat image with acceptably small netdistortion and with entirely adequate color correction includinglongitudinal, lateral and chromatic variations of the seidelaberrations. It will be noted from the drawing that the optical systemis physically quite long for its focal length. In one fomi of theillustrated embodiment, as shown, the overall length from the frontsurface of lens 44 to the final image plane is 6.487 inches, whereas thefocal length is five inches. Some of the physical length of theillustrated system has been obtained by use of the Schmidt array,inasmuch as a Schmidt system is quite long for its focal length even asa separate system.

Specific Example Illustrating Combination of Objective Lens Array 44,46, and Schmidt Lens Array 54, 56

The specific example of the following table lists representativenumerical values for the radii, thicknesses, indices of refraction andAbbe numbers of an optical system of the foregoing type, includinglenses 44, 46, prisms 48, 50 and lenses 54, 56. Elements 58, 60, whichare not necessary to the optical system of the following specificexample, will be described later. As indicated above, in the followingsystem, the focal length 5 inches, the side-to-side field-angle 38 andthe speed is 178.

When two optical systems that are separately corrected are placed intandem, additional degrees of freedom for the alignment are introduced,particularly if the intervening axial bundle is of parallel light, ashere. The first system can be displaced along the axis, or rotated, ordisplaced laterally. It will be recalled that as the stages of opticaldesign proceed toward a more highly corrected image, the optical systembecomes increasingly less dependent on the choice of the position of theentrance pupil (and therefore of the exit pupil). In the limit if theentering light is parallel and the emergent light is not only strictlyparallel but has angular magnification (as in a telescope), the positionof the pupil becomes relatively unimportant. In the case of two suchsystems in tandem, the exit pupil of the first can be regarded as theentrance pupil of the second. If neither is sensitive to the position ofthe pupil, it follows that the positioning of the first optical systemrelative to that of the second allows some freedom. In the system athand, the separate field and Schmidt groups actually are not fullycorrected but they are sufficiently well corrected to allow some freedomof relative movement. For example, objective lens group 44, 46 iscorrected for spherical aberration, coma and astigmatism for a rearstop, but do have a strongly negative (over-corrected) curvature offield. Schmidt group 54, 56, R, also is free of spherical aberration,comma and astigmatism but has strongly positive (under-corrected)curvature of field. The off-axis wave fronts therefore are divergent andconvergent in the two systems but otherwise are stigmatically corrected.Matching these curvatures of the wave-fronts results in a net flat fieldfor the overall system, notwithstanding relative movement of the systemslaterally or longitudinally. in one modification of the illustratedembodiment, this freedom allows the option of using zoom" action toobtain focus and any reasonable variation desired in focal length.

1t should be noted that in the illustrated optical system, longitudinaland lateral color aberration have been eliminated much as it isaccomplished in the case of the ordinary triplet. Because of the largeair spaces, however, and because of the need to minimize the residualcolor aberrations, while adjusting for required location the Schmidtcomponent has incorporated a cemented doublet instead of a singleelement.

Zooming Without Zoom Lens Array 58, 60

In the illustrated optical system, if zoom lens array 58, 60 is notconsidered, there are four air spaces d d d and d Inasmuch as prism pair48, 50 has no appreciable optical power, d, and d do much the same thingand can be regarded as a single parameter. Moreover, it will be recalledthat the center of curvature of the Schmidt group is at 86, a conditionwhich exists only if d, is held fixed. Nevertheless, in an alternativeform of the illustrated embodiment, longitudinal motions in d of 1- 0.5inches can be tolerated when it is desirable to move only the cementeddoublet and to omit prism pair 48, 50. The three effective parameters,namely d d l-d, and d,,, under these circumstances, allow compensationfor focal position, focal length and some third order aberrations inorder to offset changes caused either by focusing for different objectdistances or for zooming the focal length to obtain the requiredcorrection for the remaining single cosine factor in Y and 2 direction,orboth. Although, in various modifications of the illustratedembodiment, synchronized movements involving these three parameters arecontemplated for zooming focal length in one form and for aberrationcompensation in another form, as is to be expected with only three freeparameters, the aberrations become significant outside a rather narrowrange of focus.

An additional desired feature is that the sweep action of the scanmirror should be the same regardless of object distance. In other words,where mechanical simplicity is paramount, it is desired that only asingle mechanical or clectro-mechanical movement be utilized for thescan action and that the focusing for different object distances beaccomplished separately. This requires that the image size and position,both as a function of scan and as a function of object distance, remainthe same by Zooming of the air spaces for any usable object distance.For a pure zoom system utilizing only longitudinal movement of thecomponents, only the air spaces are available as parameters and indeedonly through ranges that are permitted by the mechanical details of thecamera and by non-interference of one element with another. In thepanoramic system under consideration, the air space between sweep mirror42 and forward vertex 88 of lens element 44 is held constant to preventcontact with mirror 42. 1n the illustrated system, as mentioned earlier,the only free parameters are d,, d, +d, and d.,. If vertex 88 is toremain fixed, then lens element 44 is fixed. Therefore, only lenselement 46 moves, inasmuch as prism pair 48, 50 must not movelongitudinally. As a consequence, the increment of movement in space d,is always the negative of the corresponding increment of movement inspace d Similarly, if Schmidt lens group 54, 56 moves, the associatedincrement of movement in space d, is equal to the negative of thecorresponding increment of movement in space 11,. Thus there actuallyare only two free parameters when the overall length is held fixed andonly two components are moved. In a modification of the illustratedembodiment that omits zoom lens array 58, 60, these two free parametersare adjustable in such a way as to hold image size and position atdesired values for any reasonable object plane distance and formagnification changes needed during the sweep to produce the necessaryzooming and perspective changes in the photograph.

It will be recalled that during the sweep action of mirror 42, a singlecosine factor must be obtained to compensate for loss of localmagnification in the related cylindrical projection along the Y and 2directions. (Prism pair 48, 50 compensates for the additional cosinefactor in the Z- direction). This single cosine factor is obtained by acalculated change in the scale" at the particular off axis angle of theinstant. This change in scale must be accompanied by holding the focusat image plane 71. The two free parameters above discussed then may bedetemiined by solving the necessary equations by iteration. Since therelationships also are a function of object distance, a double entry ofspacings versus object distance, where image size and position are heldindependent of object distance.

in the following table, the lens system has, at null a five inch focallength and an object distance of 25 focal lengths 10 feet 5 inches). Inone form, the total picture scan time is A second.

TABLE ll 1/s (Reciprocal Object Distance) spacing .00 .01 .02 .04 .08.16 .32

Ad, .0255 .0193 .01 31 .0000 .0290 .0963 .1792 Ad. .0255 .0193 .0131.0000 .0290 .0963 -.1792 Ad. .1726 .0978 .0669 .0000 .1658 .5992 .7535Ad, .1726 .0978 .0669 .0000 1658 .5992 .7535 Ad, .0310 .0251 .0191 .0068.0198 .0882 .1710 Ad. .0310 .0251 .0191 .0068 .0198 .0882 1 710 Ad,.1985 .1718 1441 .0854 .0510 .5002 .6580 Ad, .1985 .1718 .1441 .0854.0510 .5002 .6580 Ad, .0444 .0390 .0336 .0225 .0006 .0522 .1685 Ad,.0444 .0390 .0336 .0225 .0006 .0522 .1685 Ad, .3765 .3549 .3330 .2875.1887 .0588 .6531 Ad, .3765 .3549 .3330 .2875 .1887 .0588 .6531 Ad,.0611 .0562 .05 13 .0412 .0206 .0232 .1284 Ad .0611 .0562 .0513 .0412.0206 .0232 .1284 Ad, .6076 .5905 .5730 .5373 .4627 .2960 .1917 Ad,.6076 .5905 .5730 .5373 .4627 .2960 1917 The tabulation shows that themovement of lens element 46 is comparatively small, a consequence of thestrong optical powers of first and second lens element 44, 46. Thelongitudinal movement of Schmidt group 54, 56 is quite large, amountingto more than half an inch at the beginning and end of the picture scan,at the mean focal distance, and to more than 54 inch, for the on-axisrequirement at an object distance of 15 inches. Since most hand camerasfocus only to about three feet for a five inch focal length, theachieved result here is unusual. The movement is executed twice duringthe scan, the center being the mean position. For the object distance of25 focal lengths, the displacement of Schmidt group 54, 56 averages0.5373 in 56 second or 1.6 inches/second. The actual movement isnon-linear, however, and is of a quadratic nature resulting from thefirst variable term in the expansion of the cosine.

Zoom Lens Array 58, 60

It is obvious that in the embodiment above described, with only two freeparameters, most versatile control cannot be exercised over thevariations in the aberrations such as longitudinal and lateral color,spherical aberration, coma, astigmatism and distortion. (Many zoomsystems employ achromatized components to minimize the variations incolor correction with zooming. in this respect, any variation in lateralc'olor usually is more serious than the one in longitudinal color andcan preclude acceptable wide angle performance). In the illustratedembodiment, in order to obtain additional free parameters, zoom lensarray 58, 60 has been introduced. Normally, one would design a system ofthis type to make maximum use of all the new parameters (four radii ofcurvature, two thicknesses, one central air space if not cemented,possible aspheric surfaces, two indices of refraction and two v-values.)1n the present embodiment, however, it is desired to achieve a widezooming range without upsetting previously described performance. Zoomlens array 58, 60 is such that its external surfaces 63, 65 aresubstantially plano. Outer surfaces 54, 56 are either plano or have likelarge radii of curvature so that they have small net coma andastigmatism and possibly some spherical aberration and curvature offield. lnner surfaces 57, 59, which are substantially identical. arelarge enough to encompass the maximum dimension of the image. Thelongitudinal color that is generated by zoom lens group 58, 60 isslightly over-corrected but tolerable at f/8/0. In an alternativeembodiment, the negative and positive zoom lenses are positioned moreclosely to the Schmidt lens array, with outer surfaces of the zoomlenses constituting a shell having a radial center substantiallyconcentric with the Schmidt lens surface and inner surfaces that aresubstantially aplanatic.

1n one fonn, lenses 58, 60 are composed of lanthanum crown glass havingan index of refraction of 1.691 and a v-value of 54.7. The high v-valueminimizes the color aberration introduced into the system. The highindex of refraction, which need not fall within critical tolerances, fora given total thickness of lenses 58, 60 taken together, provides greatoptical power in a small physical space and in turn minimizes mechanicalmovement in the zoom operation.

The following radii and thicknesses of lenses 58, 60 are typical.

TABLE 111 Lens or Thickness Airspace Radius and Spacing R =plano 58 d=0.l25-' -0.010

R ,,='+3. 3 3 3 Airspace d 3250::vlr1lble R =+3. 3 33 60 d =0.650:0.0l

R =plano 1n the illustrated embodiment, lenses 58, 60 are movable. Thus,the movable lens elements are lens 46, cemented doublet 54, 56 andlenses 58, 60, the variable air spaces thereby being d d,, d,,, d d andd As was indicated before, the increment in d, remains the negative ofthe increment in d the increment in d affects the increment in d and theincrement in d affects the increment d,.

In the following table, for a 0.04 reciprocal object distance, lenselement 58 remains'essentially at null. Like the optical system of Table11, the system has an approximately five inch focal length and an objectdistance of 25 focal lengths 10 feet 5 inches) at null position. In oneform the total picture scan time is as second.

TABLE IV l/s (Reciprocal Object Distance) ir l g .00 .01 .02 .04 .08 .16.32 Ad, -.0l30 .0098 .0066 .0000 .0137 .0434 .1152 Ad, .0130 .0098 .0066.0000 .0137 .0434 .1152 Ad. .0093 .0067 .0043 .0000 .0052 .0005 .1069Ad, .0378 .0282 .0186 .0000 .0337 .0833 .0739 Ad .0586 .0441 .02940000-0589 1751 .3841 Ad .0301 .0226 .0151 .0000 .0304 .0913 .2033 Ad,.0125 .0093 .0061 .0004 .0139 .0431 .1138 Ad, .0125 .0093 .0061 .0004.0139 .0431 .l 138 Ad, .0035 .0006 .0022 .0072.0l42 .0125 .0834 Ad..0474 .0374 .0276 .0083 .0273 .0812 .0826 Ad .0918 .0773 .0627 .0334.0256 .1420 3522 Ad, .0479 .0405 .0330 .0179 .0124 .0733 .1862 Ad, .0110.0079 .0048 .0014 .0143 .0422 .1095 Ad. .0110 .0079 .0048 -.00l4.0l43.0422 1095 Ad .0134 .0 l 71 .0208 -.0278-.0400 .0495 .0159 Ad, .0753.0646 .0540 .0327 .0083 .0743 .1078 Ad .1886 .1743 .1600 .1307 .0717.0456 .2600

Ad .1000 .0926 .0851 .070l.0399 .0208 .1363 Ad, .0090 .0060 .0031 .0029.0150 .0409 .1027 Ad .0090 .0060 .0031 .0029 .0150 .0409 .1027 Ad .041 3.0460 .0506 .0599-0780 .1054 .0874 Ad, .1152 .1039 .0926 .0697-0239.0616 1474 Ad .3405 .3266 .3125 .2840 .2257 .1063 .1175 Ad .1839 .1767.1693 .l544-.l237 .0625 .0574

The reciprocal object distance 0.04 has been taken as the mean value andthe table above gives the displacements in inches from the null spacingsfor 0.04 on-axis.

in taking advantage of the possibilities introduced by the additionalfree parameters afforded by zoom lens elements 58, 60, improvedperformance is permitted by requiring a minimization of the sum of thesquares of the weighted changes in the aberrational coefficients oflongitudinal color, lateral color, spherical aberration, coma andastigmatism. The iterative solution thus cannot be compared directlywith that of Table 11, it being expected that the air space changesgenerally will be smaller in every case. However, a comparison of Tables11 and IV with respect to magnitude of air space changes makes itapparent that for object distances including and greater than 25 focallengths, only modest changes of airspace occur in Table IV even at closeobject distances.

1n the illustrated system, if inner surfaces 57, 59 were truly aplanaticin the case where zoom lenses 58, 60 are as close to the image plane asshown, they would be too curved to admit the required field of view inthe Z-direction. However, as zoom lenses 58, 60 are moved closer to theimage plane, the relative height of the paraxial on-axis ray becomesrapidly smaller. This means that spherical aberration, coma andastigmatism become smaller and smaller anyway, regardless of whetherinner surfaces 57, 59 remain aplanatic or not. It should be realizedthat spherical aberration, coma and astigmatism a plano-plano opticalplate in the rear image space are independent of the position of theplate in this rear image space. That is to say, if one introduces athick plate into the rear air space of an already designed opticalsystem, the three aberrations then introduced as a consequence of thethickness of the plate have the same computed values regardless of thelocation. In view of the foregoing, zoom lenses 58-, 60 are designedwith outer surfaces 63, 65 plano because the associated minoraberrations can be tolerated and with inner surfaces 57, 59 arbitrarilyand analogously negative and positive respectively to approach at leastto some extent the aplanatic condition. As shown, the common radius ofinner surfaces 57, 59 is such as to permit about a half-inch variationin thickness of either element, with a small uncemented central airspacethere between.

TABLE V The null spacings are:

d, 0.1656 d 0.1000 d. 1.5000 d, 2.7369 d 0.3250 d 0.6322

The four decimals are given to prevent approximation errors buttolerances are quite normal. The overall length from the front surfaceof lens element 44 to the image plane is fixed at 6.940 inchesthroughout the movement. The scale in the image plane is so adjustedthat the sweep action is the same regardless of the object distancealthough the sweep rate varies across the field, always in the same way.For zero air space, the pair constitute merely a thick plateinterpolated into the beam. However, the null air space has been takenas 0.3250 inches to allow for plus and minus variations. The focus nowextends from infinity to the 0.16 column in Table IV withoutencountering negative air space.

CONCLUSION The foregoing disclosure thus provides a novel prismarrangement for minimizing off axis perspective distortion in apanoramic system, a novel Schmidt arrangement for correcting aberrationsencountered in an associated objective lens ar rangement and a novelzoom lensarrangement in contiguity with a focal surface. Thesearrangements are useful in themselves as well as in connection with ashallow hand-held camera of the type illustrated by way of example.Since certain changes may be made in the above disclosure withoutdeparting from the scope of the present invention, it is intended thatall matter shown in the accompanying drawing anddescribed in theforegoing specification be interpreted in an illustrative sense.

What is claimed is:

1. An optical system comprising:

an objective lens;

a Schmidt lens following said objective lens, said Schmidt lensincluding a negative first component and a positive second componentwith a convex rear surface;

an aspheric surface positioned such that refracting surfaces betweensaid aspheric surface and said convex rear surface form an image of saidaspheric surface at the center of curvature of said convex rear surface;and

means for curving the fields of said objective lens and the field ofsaid Schmidt lens in opposite directions.

2. The optical system of claim 1 wherein the forward surface of saidnegative lens of said Schmidt lens is substantially plano.

3. The optical system of claim 1 wherein said objective lens includesmeans for refracting axial light rays into a substantially parallelbundle whereby the spacing between said objective lens array and saidSchmidt type lens array is not critical, so said space can accommodateauxiliary optical components of selected physical sizes.

4. An optical system defining an object space and an image surface, saidoptical system comprising: an objective lens; and, a zoom lens, saidzoom lens being in contiguity with said image surface and having a size,transversely of the optic axis, at least as large as the size of saidimage surface.

5. The optical system of claim 4 wherein said zoom lens includes anegative lens and a positive lens, both of said size, said negative lensand said positive lens are movable relative to each other for changingthe focus of said optical system.

6. The optical system of claim 4 wherein said zoom lens includes anegative lens and a positive lens, both of said size, said negative lensand said positive lens are movable relative to each other for adjustingthe image size and position produced by said optical system.

7. The optical system of claim 5 wherein said negative lens and saidpositive lens have substantially aplanatic contiguous surfaces.

8. The optical system of claim 5 wherein said negative lens and saidpositive lens have remote surfaces of relatively low power andcontiguous surfaces of relatively high power.

9. A panoramic optical system comprising: an objective lens; a Schmidtlens, said Schmidt lens including a negative first lens and a positivesecond lens with a convex rear surface; a pair of oppositely pivotableprisms positioned between said objective lens and said Schmidt lens, oneof the surfaces of said prisms having an aspheric shape; and means forforming, by refraction, an image of said aspheric shape, at the centerof curvature of said convex rear surface of said Schmidt lens.

10. An optical system defining an object field of view and an imagesurface, said optical system comprising:

an objective lens, said objective lens including a positive first lenscomponent and a negative second lens component;

a Schmidt lens following said objective lens, said Schmidt lensincluding a negative first lens component and a positive second lenscomponent; and

a zoom lens, said zoom lens positioned in contiguity with said imagesurface and havin a size, transversely of the optic axis, at least aslarge as t e size of the Image in said image surface, said zoom lensincluding a negative lens component and a positive lens component bothof said size, which move relative to each other.

1. An optical system comprising: an objective lens; a Schmidt lensfollowing said objective lens, said Schmidt lens including a negativefirst component and a positive second component with a convex rearsurface; an aspheric surface positioned such that refracting surfacesbetween said aspheric surface and said convex rear surface form an imageof said aspheric surface at the center of curvature of said convex rearsurface; and means for curving the fields of said objective lens and thefield of said Schmidt lens in opposite directions.
 2. The optical systemof claim 1 wherein the forward surface of said negative lens of saidSchmidt lens is substantially plano.
 3. The optical system of claim 1wherein said objective lens includes means for refracting axial lightrays into a substantially parallel bundle whereby the spacing betweensaid objective lens array and said Schmidt type lens array is notcritical, so said space can accomModate auxiliary optical components ofselected physical sizes.
 4. An optical system defining an object spaceand an image surface, said optical system comprising: an objective lens;and, a zoom lens, said zoom lens being in contiguity with said imagesurface and having a size, transversely of the optic axis, at least aslarge as the size of said image surface.
 5. The optical system of claim4 wherein said zoom lens includes a negative lens and a positive lens,both of said size, said negative lens and said positive lens are movablerelative to each other for changing the focus of said optical system. 6.The optical system of claim 4 wherein said zoom lens includes a negativelens and a positive lens, both of said size, said negative lens and saidpositive lens are movable relative to each other for adjusting the imagesize and position produced by said optical system.
 7. The optical systemof claim 5 wherein said negative lens and said positive lens havesubstantially aplanatic contiguous surfaces.
 8. The optical system ofclaim 5 wherein said negative lens and said positive lens have remotesurfaces of relatively low power and contiguous surfaces of relativelyhigh power.
 9. A panoramic optical system comprising: an objective lens;a Schmidt lens, said Schmidt lens including a negative first lens and apositive second lens with a convex rear surface; a pair of oppositelypivotable prisms positioned between said objective lens and said Schmidtlens, one of the surfaces of said prisms having an aspheric shape; andmeans for forming, by refraction, an image of said aspheric shape, atthe center of curvature of said convex rear surface of said Schmidtlens.
 10. An optical system defining an object field of view and animage surface, said optical system comprising: an objective lens, saidobjective lens including a positive first lens component and a negativesecond lens component; a Schmidt lens following said objective lens,said Schmidt lens including a negative first lens component and apositive second lens component; and a zoom lens, said zoom lenspositioned in contiguity with said image surface and having a size,transversely of the optic axis, at least as large as the size of theimage in said image surface, said zoom lens including a negative lenscomponent and a positive lens component both of said size, which moverelative to each other.